Back spacing mechanism



Dec. 11, 1934. H. A. AVERY BACK sPAcING MECHANISM Filed Aug. 17, 1935 INVENTOR HE N RY ALLE N AV RY BY l v my

ATTORNEYS Patented Dec. 11, 1934 UNITED STATES BACK SPACING MECHANISM Henry Allen Avery, Groton, N. Y., assignor to L. C. Smith & Corona Typewriters Inc., Syracuse, N. Y., a corporation ofvNew York Application August 17,

3 Claims.

This invention relates to improvements in back spacing mechanism for the platen carriage of a typewriting machine, and has for its principal objects to provide a back spacing mechanism which is positive and certain in operation, is of a simple and light construction especially adapting it for use in small portable typewriting machines, and will not overthrow when the back space key is quickly and violently operated. y

To the foregoing ends, and other ends which will appear from the following description of the preferred embodiment of the invention illustrated in the accompanying drawing, the invention consists in the arrangements of parts, features of construction, and combinations of devices particularly pointed out in the appended claims and hereinafter described.

In the drawing,

Fig. 1 is a fragmentary perspective view of a typewriting machine in which the invention is embodied in its preferred form;

Fig. 2 is a fragmentary View showing part of the back spacing mechanism in plan;

Fig. 3 is a detail View showing the positions assumed, at the end of the down stroke of the back space key, by those parts of the back spacing mechanism which are illustrated in Fig. 2; and

.Fig 4 is a detail'view showing in perspective the back spacing pawl or dog and associated parts.

The invention is illustrated as embodied in a typewriting machine having a platen journalled ina platen carriage 11 which travels on a carriage bed 12 held to the main frame 13 of the machine. In said machine the carriage is fed step by step in letter feed direction by an escapement mechanism or feed mechanism similar' to` that disclosed in Patent No. 1,760,828, granted February 5, 1929, to H. A. Avery and E. L. Harmon. Said mechanism comprises a rack bar 14 on the carriage; a feed pinion 15 meshing with said rack and mounted on a shaft 16 journalled in a bracket 17 held to the under side of the carriage bed; an escapement wheel 18 held to said shaft; fixed and pivoted or loose escapement dogs numbered respectively 19 and 20 and carried by a dog rocker 21 journalled on said bracket; and spring urged dog controllers 22 and 23.

The dog rocker is oscillated by a universal bar, not shown, and the carriage is normally urged in letter feed direction by the usual spring drum 24 suitably mounted in the machine frame and connected to the carriage by the usual draw cable 25. A spring 26 normally holds the dog rocker positioned as in Fig. 2 with the loose dog 20 engaged by a tooth of the escapement wheel and a part of said dog abutting a stop 27 on the dog rocker. Controllers 22 and 23 are connected by 1933, Serial No. 685,561

a spring 28, and stops 29 and 30 are provided on the dog rocker for the controllers. The improved back spacing mechanism will now be described.

A back space key lever 31 having two arms extends fore and aft of the machine adjacent the right hand side of the main frame 13 and carries at its forward end the back space key 32. Key lever 31 is pivoted on a horizontally and transversely extending pivot 33 held to a bracket 34 attached to the frame. A bellcrank lever 35, pivoted on a fore and aft extending pivot 36 carried by the frame, has an arm extending transversely of the frame toward the right hand side of the frame, which arm is provided with a substantially circular aperture 37 adjacent its outer end in which is loosely fitted the rear end of the rearwardly extending arm of the lever 31.

The bellcrank lever 35 has an upwardly extending arm from which a rigid thrust link 38 extends horizontally transversely of the machine and toward the left hand sidev of the machine to the forwardly extending arm of a second bellcrank lever 39 fulcrumed on an upstanding pivot 40 carried by bracket 17. Lever 39 is provided with a downwardly and forwardly bent lug 4l also journalled on pivot 4G to provide a double bearing for lever 39, the main body of the lever being pivoted on a reduced upper end portion of pivot 40, as shown, and lying directly under a at portionof bracket 17. Wabbling of lever 39 is thus prevented.

Bellcrank lever 39 serves as a pawl carrier for the back spacing pawl 42 which also is of bellcrank form and is pivoted on an up and down extending pivot 43 depending from the trans- Versely leftwardly extending arm of lever 39 to the left of shaft 16. Pivot 40 of lever 39 is to the right of shaft 16, and the transversely extending arm of lever 39 passes behind said shaft. Pawl 42 has a transversely leftwardly extending arm which is connected by a coiled spring 44 to the left hand end of the transversely extending arm of bellcrank 39 and isnormally engaged behind a nger 45 on bracket 17 to hold the nose 46 of the pawl out of engagement with the toothed escapement wheel 18. The nose 46 of the back spacing pawl 42 consists of a lug pendent from the forward end of the forwardly extending arm of the pawl and having one flat face turned toward thev escapement wheel and having a pocket or recess 47 therein for receiving a tooth of the escapement wheel. Said pocket is preferably formed by pressing a portion of the nose 46 laterally as shown.

A return spring 48, attached at its right hand end to frame 13 and at its left hand end to the upstanding arm of bellcrank lever 35, normally holds the several parts of the back spacing mechanisrn in their relative positions shown in Figs. 1 and 2, thekey lever normally engaging adjacent its forward end under a suitable stop 49 carried by the frame 13. A stop lug 50 extends laterally from the left hand side of the forwardly extending arm of pawl 42 at the forward end of said pawl arm, and said lug is adapted to engage a pendent stop lug 51 on bracket 17 to limit the rearward active movement of the pawl. Lugs 50 and 5l serve to prevent excess back spacing movement or overthrow movement of the pawl. Lug 5l engages the edge of the pawl in rear of lug 50 to hold the pawl to the engaged tooth of the escapement wheel.

The pocket 4'? in the nose of the pawl not only serves to prevent disengagement of the pawl from the toothed wheel during rearward movement of the pawl, but also serves to permit the body of the pawl nose to move between the engaged wheel tooth and the next following tooth to prevent over-rotation of the wheel in reverse direction during back spacing. Spring 44 serves to swing the pawl during the initial part of the downward movement of the back space key to engage the pawl nose with the adjacent tooth of the escapement wheel. The loose engagement between the key lever and bellcrank 35 compensates for the relative angular movement between these directly engaged parts.

When it is desired to back space the carriage one letter space the back space key is depressed and released. Depression of the key rocks bellcrank 35 which, through thrust link 38, rocks the pawl-carrying bell-crank 39. This rocking of the pawl carrier carries the pawl bodily rearward. During the first part of the rearward movement of the pawl its laterally extending arm is freed from engagement with finger 45, and spring 44 swings the pawl on its pivot until the adjacent tooth of the escapement wheel is received in the pocket or recess 47 in the nose of the pawl. Thereafter, as the pawl moves rearwardly it rotates the escapement wheel clockwise (as viewed in Figs. 2 and 3) slightly more than one tooth space until the parts assume the position shown in Fig. 3. During rotation of the wheel one too-th thereof clicks past the nose of the p-ivoted escapement dog 20 rocking it temporarily into the position indicated in dotted lines in Fig. 3. As soon as this tooth passes the nose of dog 20, said dog is moved by its controller 23 to, and is yieldingly held by both its controllers 22 and 23 in, the position shown in full lines in Fig. 3. When the back space key is released this tooth moves into engagement with dog 20 due to the pull of the spring drum, and the several parts assume the relative positions shown in Figs. 1 and 2.

What I claim is:

l. A typewriting machine having a frame, a platen carriage, a toothed escapement wheel reversely rotative about an up and down extending axis to back space the carriage, a bellcrank pawl for reversely rotating said wheel, a bellcrank pawl carrier upon which said pawl is ulcrumed, said pawl and carrier being fulcrurned respectively to the left and right of the wheel axis on axes parallel to the wheel axis and each having a forwardly extending arm and a leftwardly extending arm, the pawl. being fulcrumed on the leftwardly extending arm of the carrier and having a nose on its forwardly extending arm for engaging a tooth of the wheel, a spring connecting the leftwardly extending arms of the pawl and carrier for urging the nose of the pawl to an adjacent tooth of the wheel, stationary means normally engaged with the leftwardly extending arm of the pawl to hold the pawl disengaged from the wheel, a back space key, and means connecting said key with the forwardly extending arm of the pawl carrier for rocking the pawl carrier to cause the pawl to reversely rotate the wheel.

2. A typewriting machine having a frame, a platen carriage, a toothed escapement wheel reversely rotative about an up and down extending axis to back space the carriage, a bellcrank pawl for reversely rotating said wheel, a bellcrank pawl carrier upon which said pawl is fulcrumed, said pawl and carrier being fulcrumed respectively to the left and right of the wheel axis on axes parallel to the wheel axis and each having a forwardly extending arm and a leftwardly extending arm, the pawl being fulcrumed on the leftwardly extending arm of the carrier and having a nose on its forwardly extending arm for engaging a tooth of the wheel, a spring connecting the leftwardly extending arms of the pawl and carrier for urging the nose of the pawl to an adjacent tooth of the wheel, stationary means normally engaged with the leftwardly extending arm of the pawl to hold the pawl disengaged from the wheel, a thrust link extending rightwardly from the forwardly extending arm of the pawl carrier, a bellcrank lever fulcrumed on a fore and aft extendingaxis and having an upwardly extending arm to which said thrust link is attached and a rightwardly extending arm provided with an aperture, and a fore and aft extending back space key lever fulcrumed between its ends to rock up and down and having its rear end loosely engaged in said aperture for rocking the bellcrank lever.

3. In a typewriting machine having a platen carriage and a toothed escapement wheel reversely rotative to back space the carriage, back spacing mechanism for reversely rotating the said wheel step-by-step comprising a pawl carrier pivoted to swing in a plane parallel with the plane of the wheel, a sheet metal pawl pivoted intermediate its ends on the carrier to swing edgewise in a plane parallel with the wheel plane, said pawl having at one edge thereof at one end of the pawl a lug bent into a plane perpendicular to the plane of the pawl, said lug having a flat face which is turned toward the wheel and is provided with a recess to receive an adjacent tooth of the wheel, and said pawl having a projection extending outward from the opposite edge thereof at a point opposite said lug, a spring connecting the pawl and carrier to rock the pawl on its pivot in a direction to engage the recessed lug with the adjacent tooth of the wheel, stationary means normally engaged by the other end of the pawl to hold the pawl disengaged from the wheel, key operated means for swinging the pawl carrier about its pivot in a direction to cause the pawl to receive the adjacent wheel tooth in the lug recess and pull the wheel around the wheel axis in back spacing direction, and stationary means normally disengaged from the pawl and engageable by said projection and an adjacent edge surface of the pawl to arrest said rotating movement of the pawl by the carrier and hold the recessed lug to the engaged tooth of the wheel with a portion of the lug interposed between the engaged wheel tooth and an adjacent wheel tooth.

HENRY ALLEN AVERY. 

